St. Petersburg plans to install about 20 red-light cameras in August, with Tampa following soon with as many as 20 of its own. That will nearly double the digital coverage at busy Tampa Bay area intersections. ¶ State lawmakers established rules and penalties in July, with little variation between cities and counties. So no matter where that eye in the sky may be watching, here's a primer on how it works.

A laser sensor about the size of a hockey puck is embedded in the middle of each lane behind the white "stop bar" line, which signifies the beginning of a signalized intersection.

If a car crosses the sensor at 10 mph or faster after the light has turned red, a wireless signal instructs both still and video cameras mounted on a pole to start capturing images, figuring that the driver cannot stop before the front tires cross the white bar.

Some jurisdictions use mechanical sensors to measure speed.

What constitutes a violation?

The still camera takes two photographs. A violation occurs if the first photo shows the car with its front tires behind the stop bar after the light has turned red and a second photo shows the car continuing into the intersection. The video captures the whole process.

What if I enter the intersection on green or yellow but leave on red?

That is not a violation.

Are there exceptions?

There is no violation if the photo shows that a police officer ordered you through the light, you are in a funeral procession or yielding to an emergency vehicle.

What about right turns on red?

The red-light camera law specifically says drivers do not have to come to a complete stop. Turns are legal if made in a "careful and prudent manner," a vague standard that has made strict enforcement difficult. Some jurisdictions prosecute only egregious right-hand turns. In Pinellas County, traffic Judge Ben Overton has said he plans to uphold right-turn tickets only if the driver crosses the sensor at 12 mph or more, or if the turn endangers pedestrians, cars or others on the roadway. However, police officers can still ticket motorists if they fail to make a complete stop before turning right.

What are the rules for left-turn lanes?

The same as for straight-ahead lanes. If you cross the stop bar when the light is red, that is a violation. If you enter on green or yellow, you are okay, even if you make the turn on red.

What happens when the camera goes off?

The cameras send encrypted digital images to the camera vendor, where an employee views them, blows up the license tag and notifies the law enforcement agency that a violation is likely. Police employees view the images to make the final determination. If they agree that the car ran the light, a notice of violation is mailed to the registered owner. If the car is registered to multiple people, the first one listed gets the notice. This is not yet a ticket, just a notice. Authorities have 30 days after the infraction to deliver the notice.

What happens next?

The notice of violation will include images from the two still photos and a web link to the video as well. That lets the car owner see what happened. Photos show date, time, location and speed when photos were taken. Owners have 30 days to decide how to respond. If they pay $158 by check, in person or online, their driving record will not reflect the incident.

They also can submit a notarized affidavit saying that someone else was driving, listing that person's name, address, date of birth and, if possible, driver's license number. That person then gets a traffic ticket for $158 plus court costs, which brings the total to $260 to $265, depending on the county.

If the owner fails to pay the $158 or submit the affidavit within 30 days, the police agency mails a uniform traffic citation ticket, which tacks on the court costs. Failure to pay that ticket or contest it in court within 60 days will lead to suspension of license.

What if I have moved and don't receive the notice of violation or the traffic ticket?

That is not a defense. It is your responsibility to notify the Department of Motor Vehicles of your current address. When you discover that your license has been suspended, a judge has discretion to reinstate your license and waive some court costs, but that is not a given.

What if I can prove I was somewhere else and not the driver?

The law makes the registered car owner responsible for the ticket. Proving you were not driving is not a defense unless you identify the person who was driving. If you sign an affidavit identifying another driver, and that person denies it, the judge will weigh that evidence and make a ruling.

Filing a false affidavit is second-degree misdemeanor, punishable by up to 60 days in jail and a $500 fine.

Will contesting a ticket in court add to my cost?

It should not. Once you receive an actual ticket, then your fine and court costs will jump to $260 to $265, but should not rise further even if you contest the charge and lose. In addition, a judge has discretion to waive some of the court costs for a good reason. For example, you might say you never received the notice of violation and the judge can consider that.

Will a violation put points on my license or affect my insurance premium?

No. By state law, red-light camera violations do not put points on your license, even if you contest the charge or fail to pay the $158 on time. Nor can insurance companies raise your rates because of them. However, if you do not pay the $158 or submit a valid affidavit on time and receive an actual ticket, then a notation about the infraction goes on your driving record. If you then get a subsequent traffic ticket, the judge considering punishment in that case can consider your red-light violation as an aggravating circumstance.

Why are the rules more lenient when an owner pays right away?

According to the attorney general, the Legislature figured that cameras would lead to lots of tickets and could clog up courts, so the law builds in incentives for owners to pay right away and not fight. The constitutionality of that provision is being challenged.

Who gets the money?

The city or county where the camera is located gets $75 for each violation. The rest goes to the state. Court costs go to the county clerk. The camera vendor usually receives a flat monthly fee of $4,200 to $4,700 per camera. Roughly two paid tickets a day will cover that cost.

Where are cameras located?

The map on this page shows the locations of red-light cameras in the Tampa Bay area. Camera locations can move from time to time as ticket collection or accident rates change. The law requires that a roadside sign warn drivers that they are approaching an intersection with a red light camera.

This story has been changed to reflect the following clarification: Failure to stop before making a right turn on red is illegal, but cannot result in a violation via a red light camera. Police officers can still issue tickets if they see a motorist failing to make a complete stop. An earlier version of this story was unclear on this point.

A car that drives over a sensor when the light is red will trigger the video and the still camera's first image. The car must be traveling 10 mph or faster to trigger the sensor.

The still camera photographs the vehicle again as it moves through the intersection.

The two photos, plus a blowup image of the vehicle's license plate, are mailed to the vehicle owner, along with a link to the red-light camera video online.

What activates a red-light camera?

A laser sensor about the size of a hockey puck is embedded in the middle of each lane behind the white "stop bar" line, which signifies the beginning of a signalized intersection. The sensors trigger pole-mounted cameras — for video and still images — behind the intersection.

What constitutes a violation?

A violation occurs if the first photo shows the car with its front tires behind the stop bar after the light has turned red, and if a second photo shows the car continuing into the intersection. The video captures the whole process.

See who has, will have cameras

See where red-light cameras are in place across the Tampa Bay area. 6B